I recently was told by a master LAQ to cover the flange with blue painter's tape--it holds it out of the way and also serves as a very visible stop line too. You didn't say, but were there lots of seams in each block? If so, using them on the back probably did present problems. I like the idea to offer the customer a discount with an explanation. she will probably appreciate your honesty. I was recently rushing to finish a youth quilt for a friend when I got a length wise pleat on the back--of course I found it when I was almost finished. My friend was ok with it but I was embarrassed and ripped stitches for 8 hrs and re-did. Sometimes you just have to start over on things.